Rocker joint pin type CVT chain
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a continuously variable transmission (CVT) chain having link plates connected by rocker joints, a rocker pin and a seat pin being received in an insertion bore in the link plate and bearing against one another along arcuate contact surfaces. More particularly the invention relates to such a chain wherein a minimum sectional area of the link plate formed between the link plate insertion bore and the outer periphery of the link plate relative to the pulley, is greater than the sectional area formed between the link plate insertion bore and the inner periphery, and the radii of curvature of the inner rolling contact surfaces of the rocker pin and seat pin are smaller than those of the outer rolling contact surfaces. 
     2. Prior Art 
     A continuously variable transmission is generally composed of a pair of pulleys mounted on a driving shaft and a driven shaft, respectively. A plurality of frictionally driven blocks, mounted on an endless chain, are entrained on said pulleys. The pulleys have opposing conical surfaces for receiving the friction blocks of the chain. The conical surfaces of one or both pulleys can be varied in their spacing to adjust the effective diameter of the pulley. When the distance between the respective conical surfaces of either or both pulleys is changed, the distance from the axis of the pulley to the contact position of the frictionally driven blocks also changes, thereby changing the effective diameter of the pulley. The resulting structure is commonly referred to as a &#34;continuously variable transmission&#34; or CVT, because the spacing of the conical surfaces can be adjusted to any point in a continuous range. 
     The present invention relates to a rocker joint pin type CVT chain, which may be a &#34;dual row&#34; type or a &#34;single row&#34; type. The blocks are mounted on link plates connected by rocker joints having two pins that bear against one another along arcuate surfaces. 
     FIG. 1 illustrates a single row type CVT chain of the rocker joint pin type, in which a plurality of link plates L1, L2 are endlessly connected by means of a plurality of rocker joint pins P so as to form an endless transmission chain C. A plurality of frictionally driven blocks B are mounted to the link plates, in the illustrated case surrounding the link plates in positions between the successive connecting pins P. The V-shaped inclined surfaces T, T of the blocks B frictionally engage with the conical surfaces of the pulleys (not shown) so as to form the continuously variable transmission. 
     In a known rocker joint chain of this type, as shown in FIG. 3a, two connecting pins Pl, P2 together form a rocker joint pin and bear against one another at points A, A&#39;. When the chain is positioned such that the links are straight in line, the contact points A, A&#39; of circular opposing rolling surfaces A1, A2 of the two connecting pins P1, P2 are located beneath the line N-N defined by connecting the centers of the insertion bores H, H of the rocker joint pins (i.e., internally of line N-N relative to the route of the endless chain around its pulleys). The contact points A, A&#39; move upwardly from the center line N--N (i.e., outwardly of the chain route) with flexing of the connections of the link plates, as shown in FIG. 3b. 
     Consequently, with flexing of the chain, compression force is applied to the link plate inside of the center line N--N, and tensile force is applied to the link plate outside of the center line N--N, respectively. 
     A more detailed explanation can be made with reference to FIG. 3c. A tensile force F1 acts at the contact point A of the connecting pins at one joint; and a tensile force F2 acts at the contact point A&#39; in the opposite direction at the other joint as the successive chain links draw one another along the chain route. Said tensile forces F1 and F2 are shown as tensile force components Ft 1  and -Ft 2 , aligned parallel to the center line N--N; and bending moment components Fb 1  and Fb 2  acting inwardly as the chain passes around the pulley. Within the material of the link plate L, compression takes place inside of the center line N--N relative to the pulley; and tension takes place outside of the center line N--N due to the tensile component forces Ft 1  and Ft 2  as well as the bending moment forces. 
     A greater tensile force acts at the minimum sectional area portion D disposed between the pin insertion bore and the outer periphery of the link plate L than at the minimum sectional area portion D&#39; between the pin insertion bore and the internal periphery of the link plate L. 
     Nevertheless, if the link plates L in the chain C are ordinary link plates, said two minimum sectional area portions D, D&#39; have the same sectional areas. Hence, cracking is likely to occur sooner at the outer minimum sectional area portion D, where the forces are greater. 
     Furthermore, as mentioned before, the contact points A, A&#39; of the opposing rolling contact surfaces Al and A2 of the pins P1 and P2 move from the position shown in FIG. 3a, where the links are straight in line, to a flexed position shown in FIG. 3b as result of the angular displacement of successive links with flexing of the chain C. In a conventional CVT chain, the opposing rolling contact surfaces Al and A2 are composed of arcuate surfaces having a uniform radius of curvature, i.e., defining an arc of a circle; and consequently, when the chain is in a straightened position as shown in FIG. 3a, the contact points A, A&#39; are situated inwardly of the center line N--N by an amount E l . As a result, when the chain is straight, the tensile load is shifted partially to the inner minimum sectional area portions D&#39;, D&#39;, which causes the strength of said portions to decrease. 
     It would be desirable in a CVT chain of the present type to arrange the links and the connecting pins so that loads applied to the chain link plates are more nearly equalized. In this manner, the chain can withstand greater loads per unit of chain weight, and longer wear. 
     SUMMARY OF THE INVENTION 
     It is an aspect of the invention to solve the above-mentioned problems of the prior art by improving on known structures of CVT chains. In a rocker joint pin type CVT chain having a plurality of link plates connected endlessly by means of rocker joint pins, each comprising a rocker pin and a seat pin adapted to make rolling contact by means of a pair of opposing rolling arcuate surfaces, the invention provides an improvement in that the minimum sectional area formed between the link plate insertion bore and the outer periphery of the link plate is greater than the minimum sectional area formed between the link plate insertion bore and the inner periphery of the link plate. In addition, the radii of curvature of the inner rolling contact surfaces are smaller than those of the outer rolling contact surfaces. 
     As mentioned before, when the chain is flexed, bending moment forces act on the link plates, namely tensile force Ft 1  and Ft 2 , as do tensile forces. Therefore, by making the minimum sectional area formed between the link plate insertion bore and the outer periphery of the link plate is greater than the minimum sectional area formed between the link plate insertion bore and the inner periphery of the link plate, the fatigue strength at said minimum sectional area portions is increased. Furthermore, by making the radii of curvature of the inner rolling contact surfaces smaller than those of the outer rolling contact surfaces, the deviation of the contact points of the opposing rolling contact surfaces relative to the center line N--N is minimized when the chain links are oriented straight in line, thereby reducing the load applied to the inner minimum sectional area portions. 
     A primary use of the CVT chain is for an automatic transmission of a vehicle, where a relatively small chain with small link plates is desirable, but the torque to be transmitted is extremely large. The present invention provides a CVT chain having substantially increased fatigue strength owing to the above-mentioned structure, and operates well in such demanding applications. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     There are shown in the drawings the embodiments of the invention as presently preferred. It should be understood that the invention is not limited to the precise arrangements and instrumentalities shown in the exemplary embodiments, wherein: 
     FIG. 1 shows a perspective view of a continuously variable transmission chain of the rocker joint pin type; 
     FIG. 2 is an enlarged elevation of a link plate of the chain according to the present invention; 
     FIG. 3a is an elevation of a link plate of a conventional prior art CVT chain having connecting pins in a straightened position of the chain; 
     FIG. 3b is an elevation of the chain when the chain of FIG. 3a is entrained by a pulley; and, 
     FIG. 3c is an enlarged elevation of one of the link plates in FIG. 3b. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 2, a rocker pin joint according to the invention comprises a rocker pin 2 and a seat pin 3, inserted into a bore 7 formed in a link plate 1. A plurality of the link plates may be arranged in alternating configuration across the width of the chain. The respective contact surfaces 4 and 5 of the rocker pin 2 and seat pin 3 come into contact at one point 6. When the chain is in a straight tensioned state, the contact point is located inwardly of the center line N--N (below the center line in FIG. 2) by the distance E l . When the chain is flexed so as to pass around a pulley, the rolling or contact surface 5 of the seat pin 3 and the rolling or contact surface 4 of the rocker pin 2 roll over one another in contact. Thus the contact point between surfaces 4, 5 moves outwardly (or upwardly in FIG. 2) of the center line N--N. 
     Within the span of rolling contact, the radius of curvature r of the lower half of the rolling surfaces 4 and 5 is smaller than the radius of curvature R of the upper half of the rolling surfaces 4 and 5. Therefore, the amount of deviation of the contact point E l  between surfaces 4, 5 (as above defined) is relatively smaller, since said amount is calculated as follows: 
     
         r tan α=E.sub.l 
    
     where α is the angle of inclination of successive links with respect to the center line N--N. In other words, as shown in FIG. 2, point 0 (the center of the larger radius R), 0&#39; (center of the smaller radius r) and the point 0&#34; (center of the bore 7) are situated on the same line, which is inclined by the angle α relative to the center line N--N. 
     When the chain is flexed as shown in FIG. 3c, a tensile load due to a bending moment of force is applied to the minimum sectional area portion 8 between the bore 7 and the outer periphery of the link plate 1. In addition tensile loads Ft 1  and Ft 2  are applied due to the linear tension of the chain. In order to strengthen minimum section area 8 against the load, said minimum sectional area portion 8 is made larger than the counterpart minimum sectional area portion 9 formed between the bore 7 and the inner periphery of the link plate 1. This improves the fatigue strength of section 8, and the strength of the chain as a whole. 
     The invention having been disclosed, variations on the subject matter will occur to persons skilled in the art. Reference should be made to the appended claims rather than the foregoing specification in order to assess the scope of the invention in which exclusive rights are claimed.